It really depends on what format the files are saved in. If you have XP, there is a program called windows movie maker. You would need to import both of your video files, then drop them on the timeline and save the new file. You could also add transitions so that it looks like one film. Movie maker is a basic version of the kind of software you need. Other film editing software like Pinnacle or Ulead could be used for more in depth effects. If you look around the net, there are quite a few demo versions available for download.